Xitreous  -anb vitrifiable composi



Patented Jan. 14, 1 947 VITREOUS AND VITRIFIABLE COMPOSI- TIONS F jMLATTER AND METHODS OF MAKING THE SAME Harold R. Feichter, Canton, Ohio, assignor to United States Quarry Tile Company, Canton, Ohio, a corporation of Delaware No Drawing. Original application August 27, 19 42, Serial No.456,414. Divided and this application May 27, 1946, Serial No. 672,689

1 Claim. l

The disco-very and invention relate in general to compositions of matter for vitreous products and the like, and for vitrifiable bodies and the like, and methodsofmaking the same.

The discovery andinvention particularly relate to substances requiring high temperatures for vitrification, and more particularly to compositions of matter including aluminum ioxide, and this application is a division of my application, Serial No. %56,414, filed Augustfi l, 1942.

Products made by vitrifying or firing at high temperatures, body compositions having as their principal constituents aluminum oxide are used as spark plug insulators, particularly for aircraft engines, wear resistant and similar parts having extreme hardness, and for other purposes.

Spark plug insulators adapted for use in ahigh compression internalcombustion engine such as an aircraft engine or motor become increasingly difficult to produce, the higher the compression of the engine, and the tendency is always to increase the compression of an aircraft engine whenever possible,

Micahas heen used for the insulators of aircraft engine spark plugs; but most mica having therequiredspecial mineral and physical properties must be imported into the United States, the forming and machining of mica insulators is relativel costly, and the quality of mica insulators is not always satisfactory.

Mica being, a natural mineral and containing a varying amount of chemically combined water of crystallization in its composition, tends to decompose when" heated giving up its water of crystallization ,anddeteriorating in crystalline form to thatlof'an anhydrousflpowder; and thus deteriorates rapidly from its initial characteristics.when'.used'as a sparkplug insulator in a high compression engine.

With the development of higher compression motors, mica becomes increasingly unsatisfactory as aninsulator for the, spark plugs for the motors, and other substances haveJbeen used including ordinary porcelain and mullite porce- 5 lain. h

,Ordinary porcelain,"such as a composition of feldspanpure clay, a'ndjfiint fired to atemperature of 2300.to 2500 'F., constitutes a superior form ofburneol clay. product,fbut for spark plug insulator use ,hasrelatively poor resistance to the thermal. shock imposed upon the (spark plug insulators iofva high compression, motor.

Furthermoreordinaryporcelain has alow dielectric strength, particularly when hot, and is in fact an electrical conductor when'hot. Ordi- 2 nary porcelain also has insufiicient thermal conductivity for use as a satisfactory aircraft engine spark plug insulator, and furthermore is subject to attack by the lead compounds present in the combustion gases of high octane tetra ethyl lead gasolines. i V

Mullite porcelains, composed chiefly of clay and silica minerals, such as sillimanite, fired together at a temperature of approximately 2W0 F., develop into strong crystalline structures having improved mechanical strength and improved "hot dielectric strength as compared to ordinary porcelains, but still lacking sufficient thermal conductivity and chemical stabilitynecessary for use as spark plug insulators in high compression aircraft motors.

It has been determined to be desirablegforuse as spark plug insulators in high compression aircraft motors vto provide a fired composition of matter having the greatest attainable combination of the following properties: 1

l. Vitreousness to a high degree, and extremely low porosity; l

2. Hot dielectric strength in excess .of

megohmsat 1 000 F.;

3. Resistance to thermal shock so as not to be subject to fracture when quenched in water at room'temperature from a temperature of 400R; i

,4. Mechanical strength greaterthan 109,988 :lbs.

per sq. in. in compression; a

. High thermal conductivity; 7 H v Hardness and -rcsistanceto wear such that the hardness is-Q or overon Mohsf-scale;

8. Inert with common acids at normal temperatures, that .is not subject to appreciable loss in hot or cold HCI, HzSOuHNOs, or

9. Resistant to corrosion inmolten lead oxide;

10. Absorptive of radiant energy.

condensation of a :pure vzaluminaabody to {the point of complete witreousness free from porosity, and because the lackof plasticity :OfgpllIG alumina renders its formation as abody into any .,mina will be about in the same degree.

. 3 particular shape such as that of an insulator very difiicult.

By the present discovery and invention, it has been found that the presence of a very small amount of substantially any other inorganic substance in a body otherwise including substantially all alumina will produce a pronounced depression in the temperature necessary for the vitrification of the body composition, and will improve the forming adaptability. v V It has further been discovered that a combina tion of a relatively greatvariety of other substances to a total of a very small amount in a body, the remainder of which is substantially all alumina, has a more pronounced effect in depressing the vitrification temperature than when only one or two other substances with alumina are used for the body.

It has further been discovered that by using a combination of four or more other substances with alumina in the body, that the total amount of the added substances can be kept very low in proportion to the alumina and that in this way the properties of the body and the fired product are predominately those ofalumina, and stability is attained in the production of the fired products without the sacrifice of any substantial amount of the desired properties of the ,major ingredient alumina.

Plotting the effects of the various added substances on a phase rule diagram reveals a leveling off of the effects through the combination of the various added ingredients, so that instead of sharp changes affecting the combination, the changes are more gradual and the firing range bilized.

Furthermore, the addition of a relatively great variety of substances to the predominant alumina provides a factor of safety against the variations. that normally exist in the commercial forms of the substances, so that a more stable and dependable body is obtained through the use in the body composition of a wide variety of substances added to the alumina.

Also it has been discovered that regardless of the specified substance added to the alumina, if added in minute amount, theeffect on the alu- The alumina in the resultant mixture or body is over whelmingly the predominant material, and the resultantbody has substantially the properties of that of pure alumina.

-In attaining a combination of the highest degree of "the above enumerated properties for a fired composition of matterfor use as. aircraft engine spark plug insulators, it has been found preferable to use body combinations of aluminum oxide with the addition of chromium oxide in a minor quantity plus the addition of small quan-, ,tlties of other inorganic substances preferably the oxides of the other metals.

In particular the chromium oxide produces in the fired article a strong pink or rose color at room temperature. Without the chromium oxide the fired articles are white in color. The strong pink or rose color produced in-the fired article bythe chromium oxide changes when hot, as when the article is in use as an insulator in an aircraft engine spark plug, to black which imparts to the insulator the property of greater heat absorption by the absorption of radiant heat from the gases of combustion in the; engine cylinder, the radiant heat being otherwise reflected by white or coated bodies.-

. of the combination is greatly extended and sta- To the predominant alumina, the chromium oxide is added and small quantities of other substances selected from a wide variety of metallic oxides and compounds.

The total amount of the added substances should preferably not exceed 8% of the total composition, the remaining 92% being alumina. It is preferable that the total number of added substances be more than three. I

All theadded substances are selected from the following metals in their oxide or other com pound forms:

The above metals are included in groups 1, 2, 3, 4, 5, 6, '7, 8, of the periodic table of elements of matter.

. While it has been found that the presence of the alkalis of group 1 of the periodic table of ele-- ments, particularly sodium and potassium, are deleterious to the fired composition in causing a reduction in hot dielectric strength, it is a practical impossibility to avoid traces to measurable amounts of these substances in the body.

Furthermore, it has been found that a proportion, of these alkalis not in excess of 0.05% does not sufficiently deteriorate the body dielectrically to cause any seriously harmful results, and that their presence in combination with other sub stances, particularly the alkaline earths of group 12 of the periodic table of 'elements andboron,

develops low fusion combinations and intensifies the fluxing action of the mass, Therefore allowance for the presence of these alkaline substances is made in the particular body compositions of the present discovery and invention.

,The alumina in the body composition or mixture. should be in excessjof 92% and preferably in excess of 95%. Ithas been found impractical -froma firing standpoint to vitrify mixtures much in excess of alumina. However theproperties of the product are much improved as the "alumina is increased, and laboratory products have been made at temperatures of 3400 F. in I which compositions as high as 93% of alumina were vitrified, yielding an excellent producubut impractical to produce in commercial practice at present because of the exceedingly high temperature required.

The alumina is preferably in excess of 99% A1203 and as stated free from alkalis in excess of 0.05% and also free from silica in excess of 0.05%.

The silica content of the body is minimized by avoiding silica contamination in the processing, and by using silicates as little as possible in the body composition. Where calcium, magnesium, chromium, beryllium, and barium are used in the body composition, the forms of these substances may be in th compounds including fluorides, carbonates, oxides, phosphates, sulphates, etc., to avoid the silicates. All the added substances should be preferably in the dehydrated form, and free from the alkalis, lithium, sodium, and potassium.

However, by the introduction of fluorides into the body composition, silicates of the metals, such as magnesium in the form of talc may be used to a limited extent without harmful results from subsequent silica contamination, because the fluorine set free by the reaction resulting from the firing of the body composition combines with the silica to form gaseous silicon tetrafiuoride which escapes and constitutes a volatilization of the silicon.

Describing one particular composition of matter or Body composition I of the discovery and invention and the method of making the same, the principal ingredient of the body composition is calcined aluminum oxide, which before use in the compounding of the body is highly refined and freed of soluble impurities by lixiviation after being ground to a sub-microscopic grain size.

To 92 parts by weight of this purified and fine- 1y ground alumina A1203 is added and thoroughly mixed 1 /2 parts of calcium fluoride CaFz and 1 /2 parts magnesium phosphate Mg3(PO4)2.4H20, 4 parts of plastic ball clay A12Os.2SiOz.2HzO and 1 part of chromic oxide CI'203.

In the grinding or the alumina to sub-microscopic grain size, quartz stones are generally used as grinding media, and in the grinding the abrasiveness of the calcined alumina on the quartz grinding stones causes about 1 /2 to 2% of silica to be ground into the alumina so that the alumina after grinding has a composition of 98 to 98 /2 A1203 and 1 to 2% SiOz.

In the preferred manner of grinding the alumina for the bodies of the present invention, a rubber lined mill is used, and the grinding balls are formed of fired alumina, thereby avoiding the pick-up of silica in the ground alumina.

It has further been discovered that the initial calcination of the fiuxing ingredients alone or in combination with parts or all of the alumina is desirable before the final body is formed and the final firing effected.

Eutectics are formed between alumina and a combination of various other substances. However the formation of these eutectics requires initially a very high temperature, at which point the firing range of the mixture is very short due to the sudden depression of the melting point at the temperature of the formation of the eutectics.

When however the mixture is fused or calcined and then ground and re-formed, as the final body composition, upon the second heating, the sintering point is reached at a much lower temperature because of the previously formed eutectics.

A combination of many ingredients yields a superior result than when only few are used, since the eutectics formed between alumina and a wide variety of substances in combination provides a wide range of temperature over which the various eutectics are active, whereas with a lesser number, the range is correspondingly shorter.

The above described Body composition I after the second firing to a temperature of over 3000 F., produces a fired product consisting of aluminum in excess of 92%, and the oxides of the added metals, silicon, calcium, chromium, and magnesium, the fired product having desired properties as set forth herein for use as an aircraft spark plug insulator, and other purposes.

Examples of other body compositions, made according to the present discovery and invention, and processed as set forth herein to produce the improved fired product including alumina and other metallic oxides, are as follows:

Body composition II Percent Alumina, aluminum oxide 92.25 Talc, magnesium silicate 1.25 Fluorspar, calcium fluoride 2.00 Clay, aluminum silicate 3.50 Chromium oxide 1.00

Body composition III Percent Alumina, aluminum oxide 91.68 Talc, magnesium silicate 1.25 Whiting, calcium carbonate 2.57 Clay, aluminum silicate 3.50 Chromium oxide 1.00

Body composition IV Percent Alumina, aluminum oxide 92.04 Talc, magnesium silicate 1.25 Barium carbonate- 0.89 Whiting, calcium carbonate 0A4 Clay, aluminum silicate 3.50 Chromium oxide 1.00 Beryllium silicate 0.88

The embodiments of the compositions of matter and the method steps of making the same described herein are by way of example, and the scope of the present discovery and invention is not limited to the same or to the particular details thereof, but is commensurate with any and all novel subject matter contained herein which may at any time properly under the United States patent laws be set forth in the claims hereof or originating herein, and the elements of any such claims are intended to include their reasonable equivalents.

I claim:

A body composition of matter, for a fired vitreous product, including the following compounds, mixed in parts by weight:

Percent Alumina, aluminum oxide 92.25 Talc, magnesium silicate 1.25 Fluorspar, calcium fluoride 2.00 Clay, aluminum silicate 3.50 Chromium oxide 1.00

HAROLD R. FEICHTER. 

